The present invention relates generally to an automatic computing controller for controlling the water level upstream or downstream of a control gate in an open channel, such as an irrigation canal, and more particularly to a controller of this type which is constructed to operate on a cyclic basis to allow the effect of a change made in the control gate position to be observable at the location where the water level is being monitored.
In open channels, such as irrigation canals it is desirable that the water level be maintained constant or as close to constant as possible at all times. If the water level is below that constant, the users of the water may not obtain a sufficient amount of water at a desired time to satisfy their needs. On the other hand, if the water rises too much above the constant level, the excess may spill off out of the canal and be wasted. Generally, the water in an open channel is maintained at a constant or close to a constant level by adjusting a control gate, which controls the amount of water fed into the canal, to compensate for the water taken out of the canal by the water users. The control gates are raised or lowered by gate operator units.
Initially, these gate operator units were adusted manually by a canal tender or water master as they are sometimes called. More rescently, however, devices or systems have been constructed for automatically operating the gate operator to make the necessity for a man who formerly made the adjustments needed to maintain the constant water level outmoded. Generally, such devices have included a transducer located upstream or downstream from the control gate which generates an electrical signal corresponding to the actual water level at that location and a control unit which controls the operation of the gate operator in response to the signal received from the transducer.
One of the shortcomings of the prior art automatic controllers is that they have not fully or entirely satisfactorally taken into effect the fact that the water level in the canal does not change at the same instant as the control gate is moved. For example, if the transducer is located a mile or two downstream from the control gate it may take as much as two to four minutes before a change in gate position produces the corresponding change in the water level at the transducer location. This time period is often referred to as "dead time". As can be appreciated, because of the dead time period, a controller responding continuously to input signals from the transducer will always be operating "ahead of" the canal. One way to try to minimize the "dead time" period is to position the transducer close to the control gate. However, because of the turbulence in the vicinity of the control gate, this arrangement is simply not workable.
In U.S. Pat. No. 4,036,023 to K. Matsumato et al there is disclosed a flood control system for a dam which provides for measuring the actual water level of the dam and for calculating the deviation value between a set reference water level and the actual water level. Proportional position control over the gate angle is then performed in response to the calculated water deviation level and means is provided for determining the outflow of water to be discharged from the dam in response to the value obtained by this control.
In U.S. Pat. No. 4,180,083 to S. Miyaoka et al a system for controlling flow rate in pipelines connecting a plurality of reservoirs is disclosed. Flow rate Q (t) of fluid flowing from one reservoir (i) to another reservoir (j) is first calculated from the water levels H (t), H (t) of both reservoirs (i), (j) and then water level H (t+1) of the reservoir (j) at the time (t+1) is calculated from its inflow and outflow taking into account the predicted amount of demand Q (t). If the water level H (t+1) is below or over the predetermined lower or upper limitation, manipulated variables for valves and pumps installed in pipelines are regulated to control inflow of the reservoir (j) so that the required fluid-feed is satisfied while maintaining the scheduled water level of the reservoir (j).
In U.S. Pat. No. 2,041,576 to A. Suksdorf there is disclosed a system for controlling the levels of fluid bodies comprising, valve means for controlling the communication between said bodies, means responsive to level of one of said bodies for controlling the opening of said valve, means responsive to the level of the other of said bodies for controlling the opening of said valve, and interlocking means controlled by both of said level responsive means for limiting the operation of said valve by one of said level responsive means to limits determined by the other of said level responsive means.
In U.S. Pat. No. 3,466,872 to Y. Shimuzu there is disclosed an apparatus for regulating water flow in a part of a channel downstream of a gate therein, comprising a float rising and falling with the water level at a station in said channel part remote from said gate; a motor for opening and closing said gate; first and second electric motor circuits including first and second normally open switches, respectively, with said first and second circuits, when closed, causing the motor to move said gate in opening and closing directions, respectively; first control means including said float, operative to cause closure of said first and second switches when the water level at said station is below and above predetermined lower and upper limits, respectively, and to maintain said first and second switches closed until the water level at said station is restored to said predetermined lower and upper limits, respectively; and a device including a timer and operative on and during closure of either of said first and second switches cyclically to close and open the respective motor circuit after predetermined time intervals, respectively.
In U.S. Pat. No. 4,073,147 to T. Nomura there is disclosed a water gate control system which selects either the automatic mode or forced mode. In the automatic mode the gate is automatically swung depending upon the level of a stream or water-way between the upright or closing position and the or opening position by a single or double acting hydraulic cylinder in which a directly or indirectly spring loaded piston is displaced depending upon the hydraulic pressure acting on the gate, and in the forced mode, the working oil under pressure being introduced into the hydraulic cylinder for swinging the gate to and holding it in a desired angular position independently of the level.
Other known patents of interest are U.S. Pat. No. 3,498,395 to N. R. Henry; U.S. Pat. No. 3,012,373 to J. H. Willis; U.S. Pat. No. 3,338,261 to R. L. Bergeson et al; U.S. Pat. No. 3,873,002 to J. R. Davidson et al; U.S. Pat. No. 3,303,967 to W. A. Munson; U.S. Pat. No. 2,796,197 to L. G. Criddle; U.S. Pat. No. 1,582,715 to R. J. Wensley; and U.S. Pat. No. 1,744,455 to F. Duwe.
It is an object of this invention to provide a new and improved controller for controlling the position of a control gate in an open channel.
It is another object of this invention to provide a controller for operating a control gate in an open channel which is constructed to compensate for dead time.
The foregoing and other objects and advantages will appear from the description to follow. In the description, reference is made to the accompanying drawing which forms a part thereof, and in which is shown by way of illustration, a specific embodiment for practicing the invention. This embodiment will be described in sufficient detail to enable those skilled in the art to practice the invention, and it is to be understood that other embodiments may be utilized and that structural changes may be made without departing from the scope of the invention. The following detailed description is, therefore, not to be taken in a limiting sense, and the cope of the present invention is best defined by the appended claims.